This is a proposal to evaluate the long term outcomes of the SHIELD study, a network-oriented, experimental HIV prevention intervention for African American injection drug users (IDUs). Based on social influence framework with theories of social diffusion and social identity, the intervention used peers as change agents to introduce safer sex and drug norms to their social networks. The study is designed to empirically examine social processes, such as norm formation and peer influence, hypothesized to explain intervention outcomes. 224 current and former drug users were trained in the 10-session intervention. Index participants were randomly assigned to either a peer outreach or an equal-attention control condition. The indexes and their peer network members were administered pre-intervention and 3-month post intervention assessments, which will complete September 1999. Preliminary analysis of 118 participants suggests that indexes in the peer outreach condition reported fewer risk behaviors and more HIV-related discussions at the 3-month follow-up. We are requesting support to conduct 12-month, 18-month, and 24-month follow-up assessments to determine the long-term effects and diffusion of effects to 934 study participants, as well as non-participating eligible individuals for comparison. In addition to assessing long-term outcomes of the SHIELD study, we seek to identify characteristics of effective peer educators, individuals for whom the intervention was most beneficial, and factors that predict relapse of risk behaviors. We also propose to conduct urine-based screening of 3 sexually transmitted infections (STIs): gonorrhea, chlamydia, and trichomonas. In addition to their health sequelae, STIs are risk factors for HIV infection and transmission, are biological markers of HIV-related sexual behavior, and help validate self-reports of risk behaviors. The data will also used to examine associations between characteristics of sex partners and personal networks to describe sexual mixing patterns of this population.